 Zoro is a confirmed member of the Shimotsuki family. In SBS 105, Oda revealed the Straw Hat swordsman's true lineage. Whilst Roro-noa Zoro is the name he's known by, his family name on his grandmother's side is Shimotsuki. 55 years ago, the famous swordsmith, Shimotsuki Kotoburo, set sail from Wano alongside another Shimotsuki family member, Furiko, the older sister of Shimotsuki Ushimaru. They settled in the East Blue 52 years ago, with Kotoburo having a child, Shimotsuki Kushiro, the late Kuwina's father and Zoro's teacher. Meanwhile, Shimotsuki Furiko met Roro-noa Pinzoro and had a son, Roro-noa Arashi, who would later meet a woman named Terra. And Arashi and Terra would go on to have Roro-noa Zoro. This confirms Zoro's connection to various notable figures, including Shimotsuki Ushimaru, the great Damiyo of Ringo, and being a descendant of the legendary samurai Shimotsuki Ryuma. The SBS also revealed that only 10 of the 25 people who left Wano settled in the Shimotsuki village, meaning that the others may have continued exploring and may be settled elsewhere in the world. And this could be why Tashigi bears such close resemblance to Kuwina if she's also of the Shimotsuki bloodline. But that's just all speculation for now, at least we know.